Microsoft is preparing to ship its Windows Phone 8.1 update with two significant changes: a notification center and a Siri-like personal assistant. Sources familiar with Microsoft's plans have revealed to The Verge that the company is currently beta testing copies of Windows Phone 8.1 internally, with plans to fully detail its features at BUILD 2014 in April. A highly requested notification center feature will be added to the software, and we're told it's enabled by swiping down from the top of the screen in a similar way to iOS and Android.